Applications for the use of plasma are widespread, and a particular area of use is that of semiconductor device fabrication. For example, plasmas are used as dry etchants in both blanket and patterned etches. Such etches can exhibit good anisotropic and selective etching qualities, and particular plasma etches, such as reactive-ion etches, allow for etching of fine patterns with good dimensional control.
In the field of semiconductor device fabrication, plasmas are also used for material layer deposition. For example, dielectrics or conductive layers may be deposited through use of plasma-enhanced deposition. Chemical vapor deposition (CVD) can also be enhanced through the use of plasmas, for example, plasma-enhanced chemical-vapor deposition ("PECVD") processes may be used to deposit material layers such as oxides, and nitrides at low substrate temperatures. Plasmas can also be used in physical-vapor deposition or sputtering applications.
To be effective in the above-described applications, and in other applications, plasmas should have a high-density (measured as the number of electrons or ions per cubic centimeter), and should have a uniform density throughout the plasma. Furthermore, the kinetic energy of the ions should also be controlled, since, for example, excessive energy ions can cause damage to semiconductor devices with which the plasma is to react.
One type of plasma source that has been developed and commonly used is a parallel-plate plasma source. Such sources use radio-frequency (RF) power sources to generate the plasma through gas discharge. These power sources may be 13.56 MHz or may generate another frequency. Parallel-plate plasma sources, however, typically generate plasmas having densities of less than 10.sup.9 cm.sup.3, which is a relatively low density. Moreover, these plasma sources do not allow independent control of the plasma density and ion energies.
Another type of plasma source, the electron cyclotron resonance ("ECR") source, uses microwave (2.45 GHz) energy sources to generate plasmas having relatively high densities, on the order of over 10.sup.11 cm.sup.3. Although ECR sources provide good plasma density and provide for good control of ion energy, they require low pressures to operate (on the order of 0.1 to a few milliTorr). Furthermore, ECR sources, because of the use of microwave components and the required low pressure operation, are complex and expensive. In addition, difficulties arise in generating uniform plasmas over large wafer areas.
A third type of plasma source, known as an inductive coupling plasma source, uses an inductively coupled radio-frequency source to generate the plasma. This type of plasma source provides for a relatively high plasma density and operates with a radio-frequency source (typically 13.56 MHz) and thus is less complex than ECR sources. However, plasmas generated by inductively coupled plasma sources may have significant plasma density distribution nonuniformities.
Therefore, a need has arisen for a simple plasma source that generates a relatively high density plasma of substantial uniformity for various plasma-enhanced etch and deposition applications.